1. Field of Invention
This invention relates to a tuning device used to change the key of a string instrument having a neck over which extends one or more strings.
2. Description of Related Art
A capo, also known as a capo tasto or capodastro, is a device that is applied to the neck of a stringed instrument such as a guitar, banjo, mandolin, bass, ukelele and the like to depress the strings of the instrument and. thereby shorten the effective vibrating length of the strings to alter their sound.
Applying a capo to a stringed instrument commonly requires the use of both hands. This is often an awkward process requiring moving the instrument or the performer's hands or both from a playing position to another position for the installation or removal of the capo, after which the playing position must be resumed. This process can be distracting to both the performer and the audience. Therefore it is desirable to have a capo which can be easily installed and removed with a minimum of instrument or performer movement.
When a capo is applied to a string instrument, the capo depresses a string against a fret resulting in a change in string tension and variation in intonation. It is desirable to apply only the minimum pressure necessary to secure contact of the string with the fret for the capo to work most effectively. Excess pressure increases intonation loss and distortion. A capo which can apply a continuously variable amount of pressure would allow the performer to minimize intonation loss and distortion.
Typically, capos which provide pressure adjustment must be preset before use on a stringed instrument. For example, the capo described by Wilkerson in U.S. Pat. No. 4,270,432 uses a toggle mechanism and an eccentric cam for a pivot to clamp the capo to the neck of a stringed instrument. The user must adjust the cam prior to placing the capo on the instrument's neck. The pressure applied by the toggle mechanism reaches a maximum when the toggle passes a top dead-center position, after which the applied pressure is reduced. The user must also balance the amount of pressure desired when the capo is installed with the amount of pressure necessary to move the toggle mechanism past the top dead-center position. In a related example, the capo in Wilkerson's U.S. Pat. No. 4,324,165 requires the user to first adjust a screw prior to placing the capo on the instrument. In operation, a lever moves a roller bearing pivot from a first recess to a second recess. The motion of the bearing pivot presses a lower arm against the neck of the instrument, providing the clamping action. Again, the user must preset a pressure adjustment prior to installing the capo, and the selected pressure is a compromise between the pressure desired when installed and the pressure needed to move the bearing pivot from the first to the second recess.
Another problem with traditional capos is their inability to adjust the amount of pressure applied while the capo is being installed by the user. It would be preferable if pressure adjustment were continuous so the user could adapt the capo's operation to changing environment or performance needs. Both Wilkerson '432 and Wilkerson '165 must be adjusted prior to installation and are not easily adjusted during installation. Ronca U.S. Pat. No. 4,168,648 provides a capo with a clamping lever having an apex or cam. The apex must pass over a pivot axis where maximum pressure is applied before reaching a stable clamping position where a lesser pressure is applied to the neck of the instrument. No pressure adjustment is available Ronca '648.
Traditional Capos are designed to depress all of the strings of a string instrument. A capo which allows a performer to depress a subset of all strings would increase the harmonic variety available to the performer by creating pedal tones or drones.
A capo is therefore desired which can be installed and removed with a minimum of instrument or performer movement. Operation with one hand is advantageous. The capo should also continuously variable pressure which can be selected by the user while the capo is being installed.